The present invention relates to a reflective liquid crystal display element used in an image display device.
Along with rapid and wide distribution of image display devices used in the data communications field including the cellular phone, PHS, and PDA (personal digital assistants), the infrastructure is being reinforced so as to be capable of accessing easily by anyone regardless of time and place.
These image display devices are designed to be used in mobile applications, and they are required to be lightweight, thin, and low in power consumption, and the liquid crystal display elements are mainly used at the present.
The liquid crystal display elements are designed to display by changing the light transmission intensity by driving the liquid crystal molecules at an effective voltage of several volts, but since the liquid crystal is a non-luminous substance, a light source is needed.
The light source requires a larger electric power than the power for driving the liquid crystal, but by reflecting the ambient light on a reflector provided at the lower side of the liquid crystal display element and making a display, a reflective liquid crystal display element making use of the intrinsic features of the liquid crystal and extremely low in power consumption may be realized.
The reflective liquid crystal display element is now becoming one of the indispensable displays of personal digital assistants.
Also due to increase in the quantity of information, the importance of color display is increasing as the display for personal digital assistants, and in the reflective liquid crystal display elements, several color display methods by using color filter or birefringence effect are proposed.
However, in the reflective liquid crystal display, since it is designed to display by making use of the ambient light, there is a problem of dark display depending on the illumination environment.
As its countermeasure, it has been proposed to focus the reflected light in the front direction of the reflective liquid crystal display element by forming an undulated surface on the reflection plane of the reflector provided at the lower side of the liquid crystal display element.
FIG. 4 shows a structure of a reflective liquid-crystal display element in a prior art, in which a conventional reflective liquid crystal display element comprises a polarizer 50, a birefringent film 51, a liquid crystal cell 52, a glass substrate 53, a transparent electrode 54, a liquid crystal layer 55, a smoothing film 56, a reflective metal film 57, a protrusion 58, and a lower glass substrate 59.
In the reflective liquid crystal display element enhanced in brightness by increasing the reflectivity by forming an undulated surface on the reflection plane, however, since the reflective electrode surface at the interface to the liquid crystal is undulated, there is a difference in the thickness of the liquid crystal layer.
Further, since the terminal for connecting with an external circuit is a laminated structure of undulated surface, flattened layer, and transparent electrode, if the terminal pitch is 65 xcexcm, electric connection may not be sufficient, or terminals are likely to be shorted.
The reflective liquid crystal display element of the invention is used in an image display device of personal digital assistant such as cellular phone. The reflective liquid crystal display element comprises:
(a) an upper substrate having one or a plurality of birefringent films and polarizing films on one side, and an upper transparent electrode on other side,
(b) a lower substrate having an undulated layer, a reflective layer for reflecting the light, a color filter, flattening means for flattening the undulated surface, a lower transparent electrode, and a light shielding layer on one side, and
(c) a liquid crystal layer layer disposed between the side of the upper substrate having the upper transparent electrode and the side of the lower substrate having the lower transparent electrode.
The undulated layer is disposed at one side of the lower substrate, the reflective layer is disposed at the liquid crystal layer side of the side having the undulated layer, the color filter is disposed at the liquid crystal layer side of the side having the reflective layer, the flattening means is disposed at the liquid crystal layer side of the side having the color filter, the lower transparent electrode is disposed at the liquid crystal layer side of the side having the flattening means, and the light shielding layer is disposed so as to cover the conductive portion of the reflective layer at the outside peripheral part of the display unit in order to suppress electric contact between the conductive portion of the reflective layer and the lower transparent electrode in the outside peripheral part of the display unit of the reflective liquid crystal display element.
Preferably, the flattening means is disposed at the liquid crystal layer side of the light shielding layer.
In this constitution, the liquid crystal cell and the external circuit can be connected favorably. The terminal does not require the undulated layer and flattened layer. Hence, the reliability of electric connection and physical connection of the terminal and transparent electrode can be enhanced.